1. Field of the Invention
The invention relates to a method for refreshing dynamic memory cells, and to a regulating circuit for regulating the repetition rate of the refresh operation of dynamic memory cells.
2. Description of the Related Art
Memory cells of a dynamic memory circuit store information in the form of charges in capacitors which are constructed in integrated form in a semiconductor circuit. The capacitors lose their charge through leakage currents, as a result of which the information is lost after a data retention time. The data retention time is the maximum time after which the content of a memory cell can still be read out correctly.
In order to store the information items permanently, the dynamic memory cells therefore have to be refreshed at regular intervals with a refresh frequency, i.e. have the information stored therein written to them anew, so that the information is not lost.
The period duration of the refresh frequency with which the memory cell has to be refreshed depends to a considerable extent on the operating temperature and the quality of the production process. This is because both factors influence the data retention time.
In the so-called self-refresh mode of a DRAM, the memory cells are automatically refreshed without external control signals by means of internal logic. In this case, it is desirable for the current consumption of the DRAM to be minimal. One essential measure for achieving this is to make the time interval between the individual refresh cycles as large as possible, without losing data.